1. Field of the Invention
The present invention relates to an electrostatic capacitor-type inclination sensor, with a pair of differential electrodes and a common electrode arranged facing each other within an air-tight container, for detecting changes in the fluid surface level of dielectric fluid introduced into the air-tight container as changes in electrostatic capacitance corresponding to an angle of inclination. More particularly, the present invention relates to an electrostatic capacitor-type inclination sensor that does not require temperature compensation or zero adjustment.
2. Description of Related Art
It is known to provide an inclination sensor mounted on a vehicle such as a motorcycle to detect the inclination of the vehicle and control various parts of the vehicle in response thereto. FIG. 15 is a perspective view of a related art motorcycle mounted with an inclination sensor, viewed from the rear. The inclination sensor 90 attached to, for example, a stay etc. extends forward from the handlebar stem at the front end of a main frame (not shown). The inclination sensor 90 inclines integrally with the main frame, i.e. the vehicle body, regardless of where the helm of handlebars 92 is. The inclination angle is then detected and this angle is detected. An angle signal detected in this manner is then sent to an ECM (engine control module) fixed, for example, to the lower part of a seat 91 towards the rear of the vehicle and is utilized in various control.
Related electrostatic capacitor-type inclination sensors are disclosed in, for example, Japanese Patent Laid-open Publication Nos. Hei. 4-53528 and Hei. 5-14168. FIG. 7 is a vertical cross-section of a related art electrostatic capacitor-type inclination sensor, FIG. 8 is a lateral cross-section, and FIG. 9 is a perspective view of a variable capacitor section.
In the variable capacitor section, a pair of differential electrodes 11a and 11b are arranged next to each other in a horizontal direction and a common electrode plate 12 is provided parallel with the differential electrodes 11a and 11b, with a fixed gap remaining between the differential electrodes 11a and 11b and the common electrode plate 12. The differential electrodes 11a and 11b and the common electrode plate 12 are housed in an airtight container 14. The airtight container 14 is filled up to approximately half its effective capacity with a dielectric fluid 13 such as silicon oil. Each of the differential electrodes 11a and 11b and the common electrode plate 12 form variable capacitors Ca and Cb.
FIG. 10 shows an example of a circuit for converting changes in capacitance of the variable capacitors Ca and Cb into changes in d.c. voltage for a related electrostatic capacitor-type inclination sensor, with an oscillator OSC being connected to the common electrode plate 12. Each of the differential electrodes 11a and 11b are connected to capacitance/voltage conversion circuits CV1 and CV2 for converting changes in capacitance to changes in d.c. voltage. Each of the differential electrodes 11a and 11b are connected to capacitance/voltage conversion circuits CV1 and CV2 for converting changes in capacitance into changes in d.c. voltage. Output signals of the capacitance/voltage conversion circuits CV1 and CV2 are inputted to a differential amplifier DA and the output of this differential amplifier DA is a d.c. signal corresponding to the angle of inclination of the sensor.
A zero-point adjustment circuit 81 controls the capacitance/voltage conversion circuit CV2 in such a manner that the output voltage of the differential amplifier DA becomes 0V when the sensor is horizontal. A temperature compensation circuit 82 controls the amplification factor of the differential amplifier DA according to the atmospheric temperature in such a manner that an output corresponding to the angle of inclination of the sensor is obtained regardless of the temperature.
FIG. 11 is a view showing the relationship between electrostatic capacitances Ca and Cb of the variable capacitors Ca and Cb (in the following, the electrostatic capacitors of the variable capacitors are expressed as the numerals given to the variable capacitors) and the angle of inclination of the sensor, with this relationship being shown as changes of temperature and individual differences within a range shown by broken lines.
On the other hand, in the related technology, the output of the differential amplifier DA representing the angle of inclination of the sensor is a function of the difference of the electrostatic capacitances of the variable capacitors Ca and Cb. When the electrostatic capacitances of the variable capacitors C1 and C2 change according to temperature and individual differences, the difference between the electrostatic capacitances (Ca-Cb) also changes within the range of the broken lines as shown in FIG. 12.
In the above related technology, at least one of the capacitance/voltage conversion circuits CV1 and CV2 has to be zero point-adjusted by the zero-point adjustment circuit 81 for each sensor so that the output of the differential amplifier DA becomes "0" when the difference is "0." It is also necessary to carry out temperature compensation for each sensor at the temperature compensation circuit 82. However, particularly when the sensor is mounted on a vehicle such as a motorcycle, in addition to it not being easy to accurately perform zero point adjustment and temperature compensation when the vehicle is in motion, there are also increases in cost and weight.